The invention relates to a process and to an apparatus for treating waste materials, especially for recovering fuel from organic substances. More particularly, the invention relates to improvements in processes and apparatus for treating waste materials at elevated temperatures and under exclusion of air.
The quantity of domestic and industrial waste is on the increase at an alarming rate and, therefore, orderly disposal of such waste is of utmost importance and urgency. Experts in the field of waste material disposal predict that, within decades, the expenditures for disposal of waste material will match those for numerous costly public projects such as education and road building. Moreover, while the available supplies of fuel and other basic materials are steadily decreasing, waste materials contain large quantities of recoverable and reusable ingredients. This applies not only for untreated refuse but also for decomposed waste materials such as sewage sludge as well as purely biological waste materials, for example, discarded surplus agricultural products and rapes which develop in wineries, breweries and similar plants.
Recovery of valuable substances from waste materials is an important industry in many developed countries. For example, it is well known to heat dried sewage sludge in the absence of air in order to convert it into coke, oil, combustible and non-combustible gases and reaction water.
Published German patent application No. 30 42 964 of Bayer discloses a process for recovering solid and flowable fuels from biological materials. The material to be treated is heated to between 200.degree. and 600.degree. C. for intervals of time which depend upon the nature of treated material.
Published European patent application No. 0 052 334 of Bayer discloses a continuous process for treatment of solid starting materials (such as granular or pulverulent sewage sludge) which involves conveying the material to be treated through a tubular reaction vessel by a feed screw. The treatment takes up an interval of 2-3 hours, and the material is heated at a rate of 5.degree.-30.degree. C. per minute.
Published German patent application No. 36 05 638 of Hatlapa discloses a process for recovery of gases from an organic material which is admitted into the narrower end of a conical centrifuge and is pushed forwardly by the following material. Admission of air at the outlet of the centrifuge results in pyrolysis which entails the generation of low-temperature carbonization gas.
German-language publication "Korrespondenz Abwasser" (Volume 6, 1982, pages 377-381) discloses four different apparatus for continuous recovery of oil from biomass, namely a furnace which employs a screw conveyor, a rotary tubular kiln, a furnace which operates with a conveyor band and a shaft furnace. Each such apparatus provides a single treating chamber for continuous transport of waste material therethrough. The apparatus differ from each other only in the nature of means for conveying the material. The pressure which is applied to the treated material is identical in each part of the chamber; as a rule, the pressure slightly exceeds atmospheric pressure so as to ensure expulsion of low temperature carbonization gases from the chamber. The speed of transport of treated material must be changed uniformly in each and every part of the chamber. Therefore, degasification of the material can be influenced merely by changing the period of dwell of successive increments of material in the chamber and by changing the temperature in the chamber.
Published European patent application No. 0 003 803 of Solbakken et al. discloses a process and a plant for manufacturing carbonaceous solids and hydrocarbons from discarded tires. The tires are comminuted, relieved of metallic reinforcing material and subjected to pyrolysis in a revolving tubular vessel. The treated material advances continuously, first through the tubular vessel and thereupon through a cooling unit.
U.S. Pat. No. 1,674,420 to Trumble discloses a process and an apparatus for recovering oils from oil shales. The material to be treated is admitted first into a preheater, thereupon into a main treating (distilling) chamber, and finally into a cooling chamber. The treatment involves contacting the material with steam.
Australian patent No. 119,700 to Jacomini discloses a process and an apparatus for treating oil shale. Batches of oil shale are admitted alternatingly into two retorts in each of which the admitted material remains until the treatment is completed. Distillation takes place as a result of admission of preheated gaseous fluids.
Published German patent application No. 29 11 905 discloses a process for neutralization of pulverulent brown coal which is stored in bunkers. The treatment includes filling the bunker prior to sealing its contents from the atmosphere.